Journal . regular intervals of time a curve connecting level and time canbe drawn. This curve can be considered either as a time-quantity curve, or as a time-head curve, and the slope of thecurve gives for a particular instant the rate of pumping, ordischarge for the corresponding head. Thus in one test, lasting a few minutes, all the data relatingto the chosen speed are obtained. The arrangement is shewn diagrammatically in Fig. 1. T is the calibrated tank with a gauge glass or float to givethe water level, measured above the level in the sump S. Simultaneously with the water level the power
Journal . regular intervals of time a curve connecting level and time canbe drawn. This curve can be considered either as a time-quantity curve, or as a time-head curve, and the slope of thecurve gives for a particular instant the rate of pumping, ordischarge for the corresponding head. Thus in one test, lasting a few minutes, all the data relatingto the chosen speed are obtained. The arrangement is shewn diagrammatically in Fig. 1. T is the calibrated tank with a gauge glass or float to givethe water level, measured above the level in the sump S. Simultaneously with the water level the power taken by thepump must be observed, and the speed regulated. As mostpumps are driven by an electric motor, this is easily done. If the level in the sump varies or the delivery pipe is so longthat the head lost in friction is not small compared with thetotal head, the level in the former must be noted and the latterestimated or measured. These quantities are usually quite small 150 TESTING CENTRIFUGAL TESTING CENTRIFUGAL PUMPS. 151 corrections, but they will be referred to later. For the present,the simplest case as already stated will be considered. Method of Plotting and Analysing the Results. This is best explained by taking an actual example, a 6-inchbelt-driven pump running at 900 revolutions per observed quantities are :— Level in Tank above Sump Kilowatts taken Time. LeveLHead. by MotorDriving Pump. Minutes. Feet. 0 25-01 15-4 Delivery pipe 8in . (lia- i 28-64 14-5 meter. 1 31-8 13-5 Tank cross-section 15-60 14- 34-49 12-6 sq. ft. 2 36-7 11-9 Weight of 1 ft. in depth 2i 38-53 11-5 of water in tank = 975 3 40-18 10-8 lb. 3i 41-18 8-8 4 41-26 7-5 H 41-26 7-4 These quantities are shewn plotted in Fig. 2. a 6 is the head orquantity curve, according to scale used, and c ^ is the kilowattstaken by the motor. At several points such as e^, c.,, on thequantity curve, normals d?„/o, ^ are drawn to the curve (bydrawing the tangent first). The tangents of th
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